BIOMECHANICAL CHARACTERISTICS OF BRAIN EDEMA - THE DIFFERENCE BETWEENVASOGENIC-TYPE AND CYTOTOXIC-TYPE EDEMA

Some of the basic biomechanical properties of edematous brain tissue h ave yet to be clarified. Therefore we measured regional tissue complia nce and swelling isotropy/anisotropy in cat brain during development o f vasogenic-type and cytotoxic-type edema. In vasogenic-type edema ind uced by cryogenic injury, the edematous white matter showed an increas e of regional tissue compliance (indentation method), which paralleled the increase in the regional tissue water content (gravimetry). Swell ing of the white matter due to edema was anisotropic, in which expansi on transverse to the neuronal fibers caused by their dissociation was 91.1%, whereas longitudinal expansion was 2.3%. In cytotoxic-type edem a induced by cerebral ischemia for 3 h, regional tissue compliance was decreased in the area suffering energy failure, which was visualized as an area of reduced succinic dehydrogenase activity. The ischemic gr ay matter showed isotropic swelling, and morphologically, prominent sw elling of neuroglial cells. These marked differences in basic biomecha nical properties between vasogenic-type and cytotoxic-type edema shoul d be taken into account when analyzing the mechanism of edema-mediated tissue injury.